Currently, in many internal combustion engines an electronic controller is used to control the air fuel mixture delivered to a combustion chamber of a cylinder of the engine, and produce a timed ignition signal in response to sensed engine parameters to ignite the mixture in engines that are spark ignited. Generally, the timed ignition signal is delivered to a spark plug which is disposed centrally in the combustion chamber, and a flame is produced when the spark ignites the air fuel mixture. In the case of both spark ignited engines and other types of engines, for a given combustion chamber, there is a period of time, typically commenced by the timed ignition signal, and extending for a predetermined time period thereafter wherein it is expected that a desired good combustion condition will occur. Then, before the beginning of the next subsequent combustion time period for expected good combustion, there is a time interval wherein such events as combustion in other cylinders of multiple cylinder engines occur, combustion products are exhausted from the combustion chamber, and a subsequent intake charge enters the combustion chamber.
A combustion sensor, which can be an ion probe, optical device, thermocouple, or like device, is typically also located in the combustion chamber. Examples of conventional combustion sensors and systems are shown in Earleson et al., U.S. Pat. No. 5,036,669, issued Aug. 6, 1991; Maddock et al., U.S. Pat. No. 5,041,980, issued Aug. 20, 1991; McCombie, U.S. Pat. No. 5,392,641, issued Feb. 28, 1995; and Wood, UK patent application GB 2282221, published Mar. 29, 1995. In operation, a combustion sensor typically produces a combustion signal in response to the presence of a predetermined combustion condition in the combustion chamber, such as, in the case of an ion probe, the flame propagating past the ion probe. The combustion signal, typically a DC voltage signal for an ion probe, is communicated to the electronic controller via a conductive path that often includes a wiring harness or the like. In some systems, the combustion sensor and/or conductors making up the conductive path which extends from the combustion sensor to the electronic controller are located in an area of high vibration and noise generation, such as noise generated by the ignition spark in that or another cylinder, or by electro-magnetic interference from a nearby antenna. This vibration and external noise can produce a noise signal on the conductive path connecting the combustion sensor with the electronic controller, which noise signal is typically a recurring pulse signal. The combustion signal is generally also a pulse signal, and as a result, some types of noise signals on the conductive path can appear to the electronic controller as valid combustion signals.
A problem that can occur when noise signals are present on a conductive path connecting the combustion sensor and the electronic controller is that the controller may misidentify or misinterpret the noise signals as combustion signals, or read the signals together, then change the operating parameters of the engine controlled by the controller based on such erroneous signals. This is particularly problematic when the erroneous signals are such as to cause the controller to cutout a properly operating engine cylinder.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.